Niagara Emitters

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Niagara Emitters Skill

Architecture (read first): VibeUE extends Unreal's native MCP endpoint. Emitter module and renderer CRUD (add/remove/enable/reorder modules, add/remove renderers, set module/renderer inputs, search module scripts) are owned by the engine NiagaraToolsets.* toolsets, called through call_tool. VibeUE's NiagaraEmitterService was trimmed to the color/curve authoring the engine doesn't provide, plus a rapid-iteration-parameter reader.

VibeUE NiagaraEmitterService (this skill) keeps ONLY color/curve authoring + a param reader:

• set_color_tint — add/set a ScaleColor tint (handles ColorFromCurve automatically)
• get_color_curve_keys / set_color_curve_keys — read/replace ColorFromCurve keyframes
• shift_color_hue — hue-rotate a ColorFromCurve while preserving detail (best for recolors)
• get_rapid_iteration_parameters — read an emitter's rapid-iteration params

NiagaraScratchPadService authors scratch-pad module graphs:

• Create empty scratch modules on any stage
• Drop Map Get / Map Set / Op / Custom HLSL nodes
• Add typed pins, connect pins, declare module inputs/outputs
• Apply + recompile in one call

For module / renderer CRUD → engine NiagaraToolsets.* via call_tool (discover with list_toolsets / describe_toolset). For system-level operations (create system, add emitters, user params, compile) → engine NiagaraToolsets.* and the niagara-systems skill. Rapid-iteration param writes (set_rapid_iteration_param*) live on NiagaraService (niagara-systems skill).

Loading skills: skills load through the engine's AgentSkillToolset (ListSkills/GetSkills) — there is no vibeue-skills-manager tool. Run VibeUE services with execute_python_code (unreal.<Service>.<method>()); reach engine toolsets with call_tool.

⚠️ CRITICAL: Script Stages

Niagara modules exist in different script stages:

• EmitterSpawn - Runs once when emitter spawns
• EmitterUpdate - Runs every frame for emitter
• ParticleSpawn - Runs once when each particle spawns
• ParticleUpdate - Runs every frame for each particle

⚠️ Adding modules/renderers is an engine NiagaraToolsets operation — stage still matters

Adding modules and renderers moved to the engine toolsets. Discover the exact tool + schema with describe_toolset and invoke via call_tool:

# describe_toolset("NiagaraToolsets.NiagaraToolset_System")   # (find the add-module / add-renderer tools)
# call_tool(toolset_name="NiagaraToolsets.NiagaraToolset_System",
#           tool_name="<add module tool>", arguments={ ... })

Whatever the engine tool's signature, which stage a module goes in still matters — this is the #1 cause of a system that "compiles" but is invalid:

SpawnRate is an emitter module — putting it in ParticleUpdate makes the system invalid, and a compile reports only the generic "System is invalid after compilation" with no pointer to the culprit. If a compile is "invalid" after you added modules, first suspect a mis-staged module (list the emitter's modules via the engine toolset and check each module's stage). Stage strings are ParticleSpawn / ParticleUpdate / EmitterSpawn / EmitterUpdate.

For building an emitter entirely from a scratch-pad / Custom HLSL module (which IS a VibeUE operation), see scratch-pad.md.

⚠️ IMPORTANT: Parameters Exist in MULTIPLE Stages

Color.Scale Color, Velocity, Size, and other parameters often exist in BOTH ParticleSpawn AND ParticleUpdate stages!

When changing these parameters, you MUST update BOTH stages:

IMPORTANT: Use full parameter names from list_rapid_iteration_params (e.g., Constants.emitter.Color.Scale Color)

# ❌ WRONG - Only sets ParticleUpdate, color may not work correctly
unreal.NiagaraService.set_rapid_iteration_param_by_stage(
    path, emitter, "ParticleUpdate", f"Constants.{emitter}.Color.Scale Color", "(0.0, 3.0, 0.0)"
)

# ✅ CORRECT - Use set_rapid_iteration_param to set ALL matching stages at once
unreal.NiagaraService.set_rapid_iteration_param(
    path, emitter, f"Constants.{emitter}.Color.Scale Color", "(0.0, 3.0, 0.0)"
)

# ✅ OR explicitly set BOTH stages
unreal.NiagaraService.set_rapid_iteration_param_by_stage(
    path, emitter, "ParticleSpawn", f"Constants.{emitter}.Color.Scale Color", "(0.0, 3.0, 0.0)"
)
unreal.NiagaraService.set_rapid_iteration_param_by_stage(
    path, emitter, "ParticleUpdate", f"Constants.{emitter}.Color.Scale Color", "(0.0, 3.0, 0.0)"
)

Why? ParticleSpawn sets initial color, ParticleUpdate multiplies it. If you only set one, the other uses its default value and the result won't be what you expect.

Task Index

Sub-docs

• color.md — all color editing: ColorFromCurve detection, choosing the right method (shift_color_hue vs tint vs scale), curve keys, per-stage color, managing ColorFromCurve.
• reference.md — VibeUE color/curve + rapid-iteration-param readers, plus where module/renderer CRUD lives (engine NiagaraToolsets) and common property names.
• scratch-pad.md — building emitters from scratch and Custom-HLSL Scratch-Pad authoring.

Verification

Compile and save after changes (compile via the engine NiagaraToolsets tool; unreal.EditorAssetLibrary.save_asset(path) to persist). For color edits, re-read the curve keys (get_color_curve_keys) or rapid-iteration params to confirm the change landed in every stage where the param exists.